Observatory: Fix bug in field overview of a class

runtime/bin/vmservice/client/lib/src/elements/nav_bar.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library nav_bar_element;
 
 import 'dart:html';
 import 'observatory_element.dart';
 import 'package:observatory/app.dart';
 import 'package:observatory/service.dart';
@@ skipping 93 matching lines @@
 @CustomTag('library-nav-menu')
 class LibraryNavMenuElement extends ObservatoryElement {
   @published Library library;
   @published bool last = false;
 
   LibraryNavMenuElement.created() : super.created();
 }
 
 @CustomTag('class-nav-menu')
 class ClassNavMenuElement extends ObservatoryElement {
-  @published ServiceMap cls;
+  @published Class cls;
   @published bool last = false;
 
   ClassNavMenuElement.created() : super.created();
 }